The present invention relates to an apparatus for generating road information on a route over which a vehicle may move.
The term xe2x80x9croad informationxe2x80x9d is herein used to mean information on curve of a road that may be used to assist the river of a vehicle to navigate. The term xe2x80x9croutexe2x80x9d is herein used to mean a course of travel from a current position of a vehicle to a desired destination.
Navigational aids are useful to assist the driver of a vehicle in locating the vehicle""s current position and for locating and moving to a desired destination. Current navigational aid is a video image of a map, which appears on a monitor and accurately reproduces the image of a road map. The current navigational aid uses a stored map database, i.e., a digital map. The map database has data identifying all roads or a road network of a route or an area over which a vehicle may move. The roads are stored as road segments each having endpoints. The roads are categorized by highways, major roads, access roads, local streets, etc. The term xe2x80x9croadxe2x80x9d is herein used to mean a highway, a major road, an access road and a local street. The vehicle that will be discussed may be a motor vehicle such as a car, a recreational vehicle (RV), a motorcycle, a bus, a truck or other type of vehicle primarily moveable over roads.
Current vehicle navigation systems may use GPS, such as an electromagnetic wave positioning system, to determine a vehicle""s current position. They may use vehicle speed sensor, rate gyro and a reverse gear hookup to xe2x80x9cdead reckonxe2x80x9d the vehicle""s current position from a previously known position. This method of dead reckoning, however, is susceptible to sensor errors, and therefore requires more expensive sensors for accuracy and dependability.
The driver may want to know road information on the route ahead while engaged in the task of driving. Such road information may be used in cruising control or a navigational aid.
JP-A 8-194893 discloses a technique to use a map database of a navigation system to determine whether or not a curve exists ahead. The map database includes point data, in terms of coordinates, each identifying a trailing endpoint of each of road segments with respect to a direction of travel, and link data each indicative of a length along one of the road segments. The point data do not contain information as to a radius of road curve of each of the road segments. This publication teaches processing the point data to obtain a road curve index, i.e., an azimuth angle, at each of trailing endpoints of the road segments. An initiation of a road curve is determined at a point when the absolute value of the road curve index exceeds a predetermined value. A completion of the curve is determined at a point when subsequently the absolute value of the road curve index drops below the predetermined value. The curve index of a measuring point is determined as an angle between two vectors, namely, a leading vector and a trailing vector. The leading vector terminates at the measuring point and the trailing vector originates at the measuring point. A sampling distance is determined. The leading vector originates at a point before the measuring point by the sampling distance along the road. The trailing vector terminates at a point ahead the measuring point by the sampling distance along the road. The radius of road curve at the measuring point is determined by calculating the following equation,
Rn=Ln/[233 sin(xcex8n/2)]
where:
Rn is radius of road curve at endpoint n,
Ln is sampling distance at endpoint n, and
xcex8n is road curve index at endpoint n.
The sampling distance Ln is updated by the previous known radius of road curve Rnxe2x88x921 calculated at the previous measuring point nxe2x88x921. The endpoints are equidistant along a road at a predetermined distance. The sampling distance Ln results from multiplying an integer with this predetermined distance.
This known technique proves to be fairly well inenvironment where a map database stores point data identifying equidistant endpoints. It would be desirable to improve the known technique such that it is capable of using a map database, which stores point data identifying variable distant endpoints. In such a map database, road segments defined by the endpoints become longer as the stretch of straightforward portion of a road network become longer.
Accordingly, a need remains to improve the known technique in movement toward versatile apparatus for generating road information ahead a vehicle.
An object of the present invention is to improve versatility of an apparatus for generating road information ahead of a vehicle.
According to one aspect of the present invention, there is provided an apparatus for generating road information on a route over which a vehicle may move, the apparatus comprising:
a stored map database having data identifying roads on the route, said roads of said stored map database being stored as road segments each having endpoints; and
an application unit to implement a circular arc approximation type logic, which, when rendered operable, cancels data defining selected road segments that fall outside of a predetermined window about a predetermined circle approximating a predetermined road curve, determines circles, each approximating a portion of non-selected road segments, compares a radius of each of said circles with a predetermined radius value, and produces road information on acute curve in response to result of said comparing the radius of each of said curves with said predetermined radius value.